CRR Histology Lab 3 I. Connective Tissue (and blood vessels) CRR Week 3
Today we look at ordinary connective tissue (this page) and also blood vessels (on reverse side of this page).
You are encouraged to use a reference (i.e., histology atlas) for basic orientation to conspicuous features of each slide.
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Slide 2, scalp
Slide 3, skin
(REVIEW) In dermis, distinguish cells from extracellular material. Question--How much of the dermis consists of extracellular material (connective tissue matrix)?
(HARD, maybe impossible) Identify a particular connective tissue cell. Question--What types of connective tissue cells may occur in skin, or in connective tissue generally? Which ones are typically more common? Question--Can you identify any of these cell types? (Small, dark nuclei among collagen fibers may be fibroblasts; cells bigger than a typical fibroblast, with noticable cytoplasm, may be macrophages; round nuclei without evident cytoplasm, especially if there are several such nuclei close together, are probably lymphocytes.)
(REVIEW) Find collagen. Question--How does collagen stain on H&E histological specimens? Question--Where is ground substance?
(EASY) Note how the texture of collagen changes across the thickness of the dermis. Distinguish between papillary and reticular layers of the dermis. Note connective tissue "papillae" which project upward into corresponding hollows in the base of the epidermis
(HARDER) Find an arrector pili. (This inconspicuous bit of smooth muscle is eosinophilic but should look distinctly different from collagen.)
(EASY) Find adipocytes. Question--Where should you look? (Fat cells are not typically found in dermis.)
(REVIEW) Distinguish epidermal derivatives (hair follicles, sebaceous glands, sweat glands) from dermal connective tissue. Question--What kind of tissue are these epidermal derivatives?
(EASY) Find an artery and a vein. Hint: Look deep. Look for "tubes" with blood cells inside. (But note that vessels are often empty, with blood washed away during sample preparation. Also, blood may sometimes appear outside vessels, due to tissue damage during sample preparation.)
(HARDER) Find some capillaries. Hint: There should be lots, especially in the papillary layer of the dermis, but they may be extremely inconspicuous. Often a single RBC is the best clue to the presence of a capillary.
(HARD) Find a nerve. Hint: Look deep. Individual nerve fibers innervating the epidermis are typically too thin to notice. Nerves are larger bundles of many fibers (axons), all surrounded by a fibrous connective tissue sheath. Question--Do the axons in this nerve belong to sensory or motor nerve cells? Explain why.
At your discretion, you may notify an instructor for a brief oral evaluation on this material. / □______
Slide 25, cornea (front surface of eyeball)
Slide 29, tongue
Slide 61, trachea (also slide 62)
Slide 43, colon
Slide 63, pelvis of kidney
On each of these speciments, find connective tissue immediately beneath the epithelium. Also find connective tissue elsewhere on the slide. Question -- How do these connective tissues differ from one another? (Note the varying proportions of cells, collagen, and ground substance.)
If smooth or skeletal muscle occurs on the slide, can you distinguish the muscle from collagen? (Use your text or atlas to learn where to look.)
Can you find / recognize cartilage in the wall of the trachea? (Use your text or atlas to learn where to look.)
Look for white and brown fat in the renal pelvis.
At your discretion, you may notify an instructor for a brief oral evaluation on this material. / □______
ELECTRON MICROGRAPHS
Use Rhodin's Atlas of Histology (from the Learning Resources Center) or other any other collection of electron micrographs.
Rhodin's Atlas is also available online, at < http://projects.galter.northwestern.edu/rhodin/
Find several examples of connective tissue. In each example, identify cells and matrix. Within the matrix, distinguish collagen and ground substance.
Find examples of connective tissue in which you can locate one or more of the following: fibroblast, adipocyte, mast cell, macrophage, and lymphocyte.
At your discretion, you may notify an instructor for a brief oral evaluation on this material. / □______
For blood vessel exercises, see part II. on reverse side of this page.
CRR Histology Lab 3 II. Blood vessels (and connective tissue) CRR Week 3
Today we look at blood vessels (this page) and also ordinary connective tissue (on reverse side of this page).
You are encouraged to use a reference (i.e., histology atlas) for basic orientation to conspicuous features of each slide.
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Many capillaries should be present in most connective tissues (the cornea is an exception). Unfortunately, capillaries are commonly inconspicuous in most histological specimens. Question--Why are capillaries inconspicuous? (What structures would you need to see to recognize a capillary?)
Look for larger blood vessels, both arteries and veins, deeper in the body, more than a millimeter from surface epithelium.
For each vessel you find, try to see the three layers -- intima, media, and adventitia. In any artery/vein pair, the vessel with the thicker media, containing more smooth muscle, should be the artery. Arteries should also have an internal elastic lamina, which may (or may not) be clearly visible. Blood cells may or may not be present within vessels. Also note the differing appearances of endothelium, visible as cell nuclei lying at the margin between intima and lumen.
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Especially large and easily identified vessels should be present in most of the specimens listed below.
Because arteries and veins tend to travel in parallel, look for paired vessels of similar size and orientation.
Slide 20, Cerebral cortex. Look in the sulcus, in the connective tissue between the two "lobes" (gyri) of the specimen. Blood cells may appear black on this slide.
Slide 29, Tongue. Search for larger vessels deep within the skeletal muscle that comprises the body of the tongue.
Slide 34, Esophagus. Look in the submucosa, the loose connective tissue between the mucosa (the layer which includes the epithelial surface) and the muscularis externa (the thick smooth muscle layer).
Slide 39, Jejunum. Look in the submucosa, the loose connective tissue between the mucosa (the layer which includes the epithelial surface) and the muscularis externa (the thick smooth muscle layer).
Slide 42, Pancreas. Look in the bands of connective tissue which separate lobes of glandular epithelium. Here ducts should be distinguished from blood vessels. Ducts are lined by cuboidal or columnar epithelium, in contrast to the simple squamous endothelium that lines blood vessels.
Slide 43, Large intestine. Look in the submucosa, the loose connective tissue between the mucosa (the layer which includes the epithelial surface) and the muscularis externa (the thick smooth muscle layer).
Slide 54, Aorta. This specimen is a piece of the wall of the aorta, stained to reveal elastic tissue. Contraction of elastin often bends sections so the intima is on the convex surface.
Slide 55, Artery, vein, nerve. This specimen is our "ideal" example for examining blood vessel structure. The tissue has been stained to show elastin (so vessels on this slide appear different from those on standard H&E slides.)
Slide 56, Atherosclerosis. This is a pathological specimen, an artery in which the intima is abnormally thickened (and the lumen correspondingly narrowed). To appreciate intimal thickening, identify smooth muscle of the muscularis. Everything between the muscularis and the lumen is intima.
Slide 60, Lung. Recall that pulmonary circulation is distinct from systemic circulation. Because blood pressure is lower in pulmonary than in systemic vessels, the walls of pulmonary vessels are correspondingly thinner. Pulmonary arteries look like systemic veins, and pulmonary veins are more delicate still.
Slide 62, Trachea. In the loose connective tissue beneath the tracheal epithelium there may be a venous plexus, several relatively large venous vessels not paired with arteries.
Slide 63, Kidney pelvis. For this lab, ignore the kidney proper and look for blood vessels in the adipose connective tissue that fills the hilus.
Slide 91, Adrenal gland. In this specimen, look for arteries in the connective tissue outside of the gland and veins in the central medulla. (These arteries and veins are connected by narrow sinusoids between cords of adrenal epithelial cells.) Curiously, the veins in the adrenal medulla have a unique structure, with smooth muscle forming several distinct longitudinal bands.
The circulatory system serves the entire body, so blood vessels may also be found on nearly any other slide.
At your discretion, you may notify an instructor for a brief oral evaluation on this material. / □______
ELECTRON MICROGRAPHS
Find examples of capillaries or other small vessels. Note appearance of endothelium and red blood cells.
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For connective tissue exercises, see part I. on reverse side of this page.